I don’t see how that will change as more and more people publish open access. These “fake” or irreputable journals will always exist. What might change, which sounds like you’re concerned about, is you won’t be able to distinguish the good from the bad just by looking at the journal name. I argue that you still would if you cared that much, since requiring all open access will mean that a new (maybe largely overlapping) set of journals will become the new “big shot” journals, and you’ll just need to know their names.

How do you know that reliable papers that are currently subscription based won’t become less reliable if they are encouraged to move to an OA model like this legislation would?

Why would they? This is my main point. The scientists doing the work will not change. The scientists reviewing the work will not change. Only the name and the fee structure will change. Reviewers and editors are who determines the quality of a journal’s papers, and reviewers are already totally unpaid, even for super big shot journals. This will not change under this model. Nothing will change except for how the money is used.

There are a lot of “what ifs” that need to be addressed before encouraging OA journals more than they already are.

What are they? The ones above seem fairly predictable to me, as a working scientist, but I’d love to hear other perspectives.

Sure, the worst leading scientists will know what is BS and what is not, but everyone else won’t have it so easy.